This invention relates generally to weighing devices, more particularly, to conveyor belt scales of the weighbridge type, used for weighing material transported along a conveyor belt.
Conveyor belt scales are used for continuous weighing of bulk materials transported along the conveyor belt. Examples of such materials are coal, aggregate, slag, or wood chips among others.
In general, conveyor belt scales employ rollers or idlers that are inserted into the conveyor system, either in place of an existing idler assembly or in addition to the existing idlers. The conveyor belt rests on the idlers and the material, like coal for example, passes over the idler assembly causing a downward deflection of the system. Generally, the idler assembly is cooperatively connected to a weight sensor. The weight sensor, depending upon the construction of the particular weighing device, converts the downward deflection into a weight measurement. Ideally, a weighing device would combine the weight with a determination of the speed of the moving conveyor belt to yield a rate of flow of material as well as the total weight of the passing material.
A typical weighing device of this type is disclosed in U.S. Pat. No. 4,682,664 to Kemp. However, this invention has several disadvantages. For example, this design mounts between conveyor frame members and is therefore limited in placement. Installation is more difficult and time consuming. Also, this type of device employs two (2) load cells designed for platform weighting. The load cells are mounted under a modified idler and receive the load force at a single point. The Force generated by the radial movement of this idler (tortional force) is transmitted to the load cell is seen as a weight the same as the weight of the material being weight. For example, a portion of the tortional movement of the idler is sensed as a downward motion on the weighing apparatus and the tortional movement therefore interferes or adds to the actual weight of the passing material and can give inaccurate weight determinations.